When you switch to your "own" (assuming you meant production id/secret) are you also switching your calls to production buy()
<script src="https://wallet.google.com/inapp/lib/buy.js"></script>
Update:
Useful info referencing @Danprime's comment:
- Chrome Apps -> Wallet for Digital Goods
For Apps, you must call buy() with an extra parameter called parameters. This parameter currently has one field, env, which specifies the environment in which to process a payment. You can set this field to either prod (production server that accepts real credit cards), or sandbox (test server that accepts test credit cards to simulate transactions). The default setting is sandbox.