diff --git a/R/crosswalk_data.R b/R/crosswalk_data.R
index beeb6cf..3996fcc 100644
--- a/R/crosswalk_data.R
+++ b/R/crosswalk_data.R
@@ -724,8 +724,7 @@ apply_single_crosswalk <- function(
       dplyr::across(dplyr::all_of(geoid_column), as.character)) |>
     dplyr::left_join(
       crosswalk,
-      by = stats::setNames("source_geoid", geoid_column),
-      relationship = "one-to-many") |>
+      by = stats::setNames("source_geoid", geoid_column)) |>
     tidytable::summarize(
       .by = dplyr::all_of(group_cols),
       ## count variables we take the sum of the weighted count variable
diff --git a/R/get_crosswalk.R b/R/get_crosswalk.R
index 144d1af..df8e55d 100644
--- a/R/get_crosswalk.R
+++ b/R/get_crosswalk.R
@@ -262,6 +262,21 @@ get_crosswalk_single <- function(
       geocorr_version = geocorr_version)
   }
 
+  # If the internal function returned an empty tibble (e.g., failed download),
+  # return early with a warning
+
+  if (ncol(result) == 0 || nrow(result) == 0) {
+    warning(
+      "No crosswalk data was returned for ",
+      source_geography, " ", source_year, " -> ",
+      target_geography, " ", target_year,
+      ". The download may have failed. Check your IPUMS_API_KEY and network connection.")
+    return(list(
+      crosswalks = list(step_1 = tibble::tibble()),
+      plan = NULL,
+      message = "Crosswalk retrieval failed. No data returned."))
+  }
+
   # Retrieve metadata from internal function (if present)
   internal_metadata <- attr(result, "crosswalk_metadata")
 
diff --git a/R/get_nhgis_crosswalk.R b/R/get_nhgis_crosswalk.R
index 979e660..2dbf6af 100644
--- a/R/get_nhgis_crosswalk.R
+++ b/R/get_nhgis_crosswalk.R
@@ -527,8 +527,7 @@ get_nhgis_crosswalk <- function(
     source_geography,
     target_year,
     target_geography,
-    cache = NULL,
-    api_key = NULL) {
+    cache = NULL) {
 
   if (is.null(cache)) { cache_path = tempdir() } else {cache_path = cache}
 
@@ -720,6 +719,20 @@ variable. Get your key at https://account.ipums.org/api_keys") }
       httr::add_headers(Authorization = api_key),
       httr::write_disk(zip_path, overwrite = TRUE), overwrite = TRUE)
 
+    # Check HTTP response status
+    status_code = httr::status_code(response)
+    if (status_code == 401 || status_code == 403) {
+      stop(
+        "NHGIS API returned HTTP ", status_code, " (authentication failed). ",
+        "Your IPUMS_API_KEY may be invalid or expired. ",
+        "Check your key at https://account.ipums.org/api_keys")
+    }
+    if (status_code != 200) {
+      stop(
+        "NHGIS API returned HTTP ", status_code, " for crosswalk ", crosswalk_sub_path, ". ",
+        "This crosswalk may not be available from NHGIS.")
+    }
+
     # Check what's in the zip before extracting
     zip_contents = safe_unzip_list(zip_path)
 
diff --git a/README.Rmd b/README.Rmd
index b663855..dae7fa2 100644
--- a/README.Rmd
+++ b/README.Rmd
@@ -22,11 +22,12 @@ devtools::load_all()
 
 ## Overview
 
-This package provides a consistent API and standardized versions of crosswalks to enable consistent approaches 
-that work across different geography and year combinations. The package also facilitates
-interpolation--that is, adjusting source geography/year values by their crosswalk weights and translating
-these values to the desired target geography/year--including diagnostics of the joins between source data
-and crosswalks.
+This package provides a simple API and standardized versions of crosswalks to enable consistent, programmatic 
+approaches that work across different geography and year combinations. 
+
+The package also facilitates interpolation--that is, adjusting source geography/year values by their crosswalk 
+weights and translating these values to the desired target geography/year--including diagnostics of the joins 
+between source data and crosswalks.
 
 The package sources crosswalks from:
 
@@ -43,14 +44,14 @@ The package sources crosswalks from:
 
 ## Installation
 
-```{r, eval = FALSE}
+```
 # Install from GitHub
 renv::install("UI-Research/crosswalk")
 ```
 
 ## Quick Start
 
-First we obtain a crosswalk and apply it to our data:
+We obtain a crosswalk and apply it to our data:
 ```{r}
 library(crosswalk)
 library(dplyr)
@@ -177,8 +178,8 @@ The list contains three elements:
 | `plan`       | Details about what crosswalks are being fetched              |
 | `message`    | A description of the crosswalk chain          |
 
-### Multi-Step Crosswalks
 
+### Multi-Step Crosswalks
 For some source year/geography -> target year/geography combinations, there is not a single direct crosswalk.
 In such cases, we need two crosswalks. The package automatically plans and fetches the required crosswalks:
 
@@ -230,18 +231,6 @@ you can omit a call to `get_crosswalk()` and specify the needed crosswalk parame
 to `crosswalk_data()`, which will pass these to `get_crosswalk()` behind the scenes. Or you
 can call `get_crosswalk()` explicitly and then pass the result to `crosswalk_data()`.
 
-### Column Naming Convention
-
-The function auto-detects columns based on prefixes:
-
-| Prefix | Treatment |
-|-------------------------------|-----------------------------------------|
-| `count_` | Summed after weighting (for counts like population, housing units) |
-| `mean_`, `median_`, `percent_`, `ratio_` | Weighted mean (for rates, percentages, averages) |
-
-You can also specify columns explicitly via `count_columns` and `non_count_columns`. 
-All non-count variables are interpolated using weighted means, weighting by the allocation factor from the crosswalk.
-
 ## Supported Geography and Year Combinations
 
 `get_available_crosswalks()` returns a listing of all supported year-geography combinations.
@@ -274,7 +263,6 @@ result <- get_crosswalk(
 
 
 ## Citations
-
 Cite the organizations that produce the crosswalks returned by this package:
 
 **For NHGIS**, see requirements at: https://www.nhgis.org/citation-and-use-nhgis-data
@@ -283,8 +271,8 @@ Cite the organizations that produce the crosswalks returned by this package:
 
 > Missouri Census Data Center, University of Missouri. (2022/2018). Geocorr 2022/2018: Geographic Correspondence Engine. Retrieved from: https://mcdc.missouri.edu/applications/geocorr2022/2018.html
 
-**For CTData**, a suggested citation (adjust for alternate source geography):
+-   **For CT Data Collaborative**, a suggested citation (adjust for alternate source geography):
 
-> CT Data Collaborative. (2023). 2022 Census Tract Crosswalk. Retrieved from: https://github.com/CT-Data-Collaborative/2022-tract-crosswalk. 
+*CT Data Collaborative. (2023). 2022 Census Tract Crosswalk. Retrieved from: https://github.com/CT-Data-Collaborative/2022-tract-crosswalk.*
 
-**For this package**, refer here: https://ui-research.github.io/crosswalk/authors.html#citation
\ No newline at end of file
+-   **For this package:** https://ui-research.github.io/crosswalk/authors.html#citation
\ No newline at end of file