Download link not being activated for customer after payment complete

My cart went down a year ago. I suspect it was hacked. Tried to fix it and finally decided to start fresh with 157C. It installed without a hitch, after a few errors on my part I got it to connect to the database. All my products are there. All products are downloads. Everything is working but the customer is not getting a download link after a successful payment. I get the email that it was paid for. The order status goes to processing, but no link to download nor is it available in his account orders screen. I turned on debug for Paypal, looked at the 16 emails I got - it appears everything is OK but there may be something in those debug emails that i don't recognize as a problem

Download links are controlled by order status configuration in your store. So as long as the payment module sets the order to an order status that you've configured to allow downloads for, the links will show. (Assuming your template isn't out-of-date and doesn't have download stuff hacked out of it by someone who didn't understand Zen Cart digital products when they created the template or altered template files for some other reason.)

If the order status is set to 2-Processing, what are your attribute download settings set to?
Particularly: Admin->Configuration->Attribute Settings->Downloads Controller Order Status Value >= lower value
is it set to 2 (for 2-Processing) ?

Also see: https://docs.zen-cart.com/user/products/downloads_activating/

Title Value Action
Enable Downloads true
Download by Redirect true
Download by streaming false
Download Expiration (Number of Days) 3
Number of Downloads Allowed - Per Product 3
Downloads Controller Update Status Value 4
Downloads Controller Order Status Value >= lower value 2
Downloads Controller Order Status Value <= upper value 4
Enable Price Factor true
Enable Qty Price Discount true
Enable Attribute Images true
Enable Text Pricing by word or letter true
Text Pricing - Spaces are Free 1
Read Only option type - Ignore for Add to Cart 1

I have not modified anything except the welcome page....Tagline her,,,,blahblah,,,

Okay, then the next thing to check is that the download product actually has a valid download attached to it.

Unfortunately, if it didn't, then it won't automatically attach to existing orders. You'd have to purchase it again to test that.

At the bottom of the Attribute controller page there is a section Downloadable products. I put the filename in and then insert the days (2) and counts (2) and it goes back to blank filename and back to 3 days, 3 count. I can't change it...
I don't even want to look right now but I'm thinking I have 2700 products with no filename associated.:blush:

I even set the price at free which would not be affected by Paypal IPN.

If you go to Catalog > Downloads Manager, it will warn you if files are missing.

Perhaps the storefront processing should be updated to not offer that download (maybe disabling the associated product with an email to the store-owner?) if the download file isn't valid.

I have green dots in the attribute controller and the download manager

By chance are you using an old template? There was a change to one of the data structures - see Release Specific Upgrade Considerations

https://docs.zen-cart.com/user/upgrading/release_specific_upgrade_considerations/

for Zen Cart 1.5.6

Just another three cents.

You state you used a new 1.5.7c and a database from a year ago. Did you ever use the zc_install to upgrade the old database to meet 1.5.7c?