I think you are trying to combine several steps at once and it is not working.
You need to break it down into steps
Step 1 — get the collections._id into a variable.
The nice thing is you can print to the console, using ‘console.log()’, the result to confirm you got the correct _id.
How are you getting the Stores/Colletions._id?
Step 2 — now that you have the correct id, use it to then query the ‘Stores/Products’.
If you still have a problem, then we can troubleshoot step 2.