j"19HxigV4QyBv3tHpQVcUEQyq1pzZVdoAutLÝ10MB seems to be the limit now for any miner running the Merchant API. However many kiddy miners are out there so anything beyond 100kb I think still means you'll have to wait a few blocks before a serious miner steps up.
text/plaintext twetch_twtext_1591093643492.txt|"1PuQa7K62MiKCtssSLKy1kh56WWU7MtUR5SET twdata_jsonnullurlnullcommentnullmb_user74reply@29ed8e295f4237eb9e05b28f130bf6d17550a11af6361b42b0ce9fb2bb70ee98typepost timestampnullapptwetchinvoice$8e3dc240-ac31-479d-82db-7494ce7fba3b|"15PciHG22SNLQJXMoSUaWVi7WSqc7hCfva
BITCOIN_ECDSA!1vqoLmo15jcBx3GmfzchbPpfxuqSGZiA6LXIFTxW7cxSk824n87XukFLf/x9RhlPAHds/rA4fpVcDgVZyYonbtkksAK7TKVvQQMbGsS2ME9EOmHCpgqRX1FCLo=
https://whatsonchain.com/tx/ee46cc58510c88ac02df258fea5a93bb17a2a512473c17d39335d2523db0833c