Troubleshooting Invalid Base64 Strings

Most decoding failures come from hidden whitespace or characters outside the Base64 alphabet. Normalize the input by trimming spaces, removing line breaks, and verifying that only letters, numbers, plus, slash, or equals signs remain.

Another common issue is double encoding. If a payload is encoded more than once, the output often includes unexpected padding or non-printable characters. Decode step by step to confirm the expected result at each stage.

Finally, confirm that the string was produced with the same variant you expect—standard Base64 versus URL-safe Base64 use different characters. Base64decode highlights invalid inputs immediately so you can correct them before they break integrations.