j"19HxigV4QyBv3tHpQVcUEQyq1pzZVdoAutL¸I'd guess it's based on the signature given.
You can't sign from my keys.
I bet you could discern more details by looking at the Twetch SDK:
https://www.npmjs.com/package/@twetch/sdk
text/plaintext twetch_twtext_1590520826710.txt|"1PuQa7K62MiKCtssSLKy1kh56WWU7MtUR5SET twdata_jsonnullurlnullcommentnullmb_user622reply@780f56e2eea6f9e5a58784e2f90927fb69fd3e588d1a1a44c35aa83f4a00500dtypepost timestampnullapptwetchinvoice$290caaf0-9916-4cb4-be15-29b884c20b62|"15PciHG22SNLQJXMoSUaWVi7WSqc7hCfva
BITCOIN_ECDSA"1Eyk15KEeYX9JwH8e98pqpX3kTUuY9d43CLXH4IQQB1GAHngjU5Ugjvt6fqq/hmEi+vwvkYza71KUO6SOhKEc6m4fnLmaQzhoIiaiwAv/J/t+MncfH+7z439qc4=
https://whatsonchain.com/tx/31dd40c01ba40cee2e6a628f03874f755fec572ccc16c7773059b82d66823322