UBL with embedded PDF

Hi,

We are working on the creation of UBL files (invoices) with embedded PDF. The PDF must be encoded in base64. We managed to do this using the code

LsBase64Content is string = Encode(fLoadBuffer(LsFileName), encodeBASE64)

When we test our UBL files on https://v2.validex.net/ then mostly we get the answer 'Length of base64 value must be a multiple of four'. So approximate 1 on 4 invoices are passing the test because the length of the string is a multiple of 4.
We also tried with Crypt but this gives exactly the same result.

LsBase64Content is string = Crypt(fLoadBuffer(LsFileName),"",compressNone + cryptNone, encodeBASE64)

How can we fix that the length is a multiple of 4 and that the PDF can be retrieved by any other software?

Thank you for your advice!

Regards,
Joris