Due to special situation, we used TurboTax to prepare and had to file by mail instead of e-file for 2018. Now I'm getting this error code saying either my AGI or pin is not matching with last year. I've double check the AGI that it should be correct, how would I have a pin to match while I didn't e-file using Turbo tax, this way of verification is really ridiculous.
Unfortunately, if there is an AGI mismatch and there is no pin, you will have to mail your 2019 return.
See this TurboTax FAQ on how to find your AGI
https://ttlc.intuit.com/replies/3301618
You can get free 2018 tax transcript from the IRS
https://www.irs.gov/individuals/get-transcript
If you filed late last year there is a good chance that the 2018 AGI never was entered into the e-file database. Try using 0 (zero) for the AGI.
If you filed an amended return use the AGI on the first filed tax return.
If it continues to reject then the AGI in the IRS database might be in error. Mail filing is the only option.