Why cookies can't be imported
Merca does not support cookie import or export. Sign in from the store window and configure TOTP for the store to reduce phone-based verification steps.
Merca cannot import or export cookies.
Pasting cookies from another browser—or buying someone else's and loading them here—moves an existing login onto a different device and IP. The platform will see a mismatch, and that can put the store at risk. A cookie file is the login. Sharing it or buying it is unsafe.
Sign in from the store window. Follow How to add a store, fill in the username and password, click Launch, and sign in there. After that, the store stays signed in the next time you launch. You don't need a cookie file to move the login. See How password autofill works.
If typing a two-step code every time is a hassle, set up two-step verification on that store and copy the code in Merca when asked. For Amazon, see How to set up Amazon two-step verification. You can also set up a passkey: How to set up an Amazon Passkey.