Under time pressure, confirm whether the receiving system expects raw Base64, a data URL, URL-safe Base64, or unpadded output. Those forms are not interchangeable in every context. Encode the exact source bytes, then decode the result independently and verify a short representative sample. If the content is sensitive, use a trusted local tool rather than an unknown website. A quick conversion is only useful when it matches the receiver's format and round-trips without data loss.
Akousa