Stellar memo rejected for not being int64

[abrkn]

Stellar memos can be a variety of formats, unfortunately, including plain text:

Memo
The memo contains optional extra information. It is the responsibility of the client to interpret this value. Memos can be one of the following types:

MEMO_TEXT : A string encoded using either ASCII or UTF-8, up to 28-bytes long.
MEMO_ID : A 64 bit unsigned integer.
MEMO_HASH : A 32 byte hash.
MEMO_RETURN : A 32 byte hash intended to be interpreted as the hash of the transaction the sender is refunding.