diff --git a/docs/api.md b/docs/api.md
index fa32bf2aa..f4119e4c1 100644
--- a/docs/api.md
+++ b/docs/api.md
@@ -58,6 +58,10 @@ fields:
 - `custom_fields`: Array of custom fields & values, specified as
   `{ field: CUSTOM_FIELD_ID, value: VALUE }`
 
+!!! note
+
+    Note that all endpoint URLs must end with a `/`slash.
+
 ## Downloading documents
 
 In addition to that, the document endpoint offers these additional