Base64 Decode Failed
Base64 decoding fails when the input contains characters outside the expected alphabet, incorrect padding, or the wrong variant (standard vs Base64URL). JWT segments and data URLs often require URL-safe decoding.
Standard vs URL-safe
Standard Base64 uses `+` and `/`. Base64URL uses `-` and `_` and often omits `=` padding. Using the wrong decoder for JWT or URL data produces garbage or errors.
Padding
Length should be a multiple of 4 after padding with `=`. Some APIs strip padding — try re-adding `=` to reach a multiple of four.
Not encryption
Base64 is encoding, not encryption. Anyone can decode it. Do not use Base64 alone to protect secrets.