I have to convert the public key from pkcs#8 to pkcs#1. I have followed this article:

https://community.intersystems.com/post/format-public-key-when-using-rsaencrypt-method-systemencryption-or-systemencryptionrsaencrypt

Now I can encrypt the string, but the service returns that the api_key must be given in the request. I almost have it.

I have checked that question, but I don't understand what happens.

Finally I have used this instruction "openssl rsautl -in fileIn.txt -out fileOut-enc.txt -pubin -inkey public.key -encrypt" using $ZF(-100) and having OpenSSL installed on the server and it works.

I want to do it with Encryption methods, there must be a way to do this with COS and not using shell instructions, right?

Sorry, I got the error with RSAGetLastError(). Is this:

error:0906D06C:PEM routines:PEM_read_bio:no start line;