Hey I had a similar problem (same error message, but in my case the TRNSTYPE header was actually present in the IIF file. Also perhaps more importantly the IIF exports were not from PayPal but a different program.) Since older IIF files generated in the same way had been working fine before the QB 2019 update, I simply bypassed the data validation in the Import IIF QB dialog box. At the bottom of the IIF import dialog box there is a link that says "Import for me. I will fix it later." - this link allows you to attempt the import without data validation. In my case, the IIF imported just fine.
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