Do you have dimensions on the products ie (products_weight [ this is built into Zen Cart]; products_height; products_width; products_length)?
If so what are they for product 1997?
The problem is not the 36 items, it's that the combined size or weight is calculated as larger than Australia Post will handle. So a valid quote is not returned.
I have a version 2.5.3 on my GitHub at
https://github.com/OldNGreyBMR/aupos...ags/v2.5.3.zip
It is backwardly compatible with PHP7.
Please try it on your
TEST system (
NOT production). Once the files are copied over, you will need to uninstall and reinstall each module and add your API code and tax rates.
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