Hi Abdul_Wahab_abbasi ,
Apologies for any inconvenience caused.
I've just tested the endpoint and it's working properly. All the inventories were returned, and no errors were triggered.
Which versions of ATUM free and ATUM add-ons have you installed?
If they are up to date, please try deactivating all plugins except ATUM, the ATUM-related add-ons, and WooCommerce, and switch to a default theme as Storefront.
If the endpoint starts working then, try reactivating your plugins sequentially until you find which one is causing the issue.
Best Regards,
José Andrés