If you can only buy $100 on Coinbase, it's likely due to limits associated with your Coinbase account. There are several factors that can influence these limits:

1. **Account Verification Level**: Coinbase imposes different buying limits based on the level of verification completed on your account. If your account is not fully verified, you might be restricted to lower purchase amounts. Completing identity verification by providing additional documents can help increase these limits.

2. **Payment Method**: The type of payment method linked to your Coinbase account can also affect buying limits. Credit and debit card purchases usually have lower limits compared to bank account transfers.

3. **Account Age**: New Coinbase accounts often have lower buying limits. As your account gets older and you continue to trade and make transactions, these limits may gradually increase.

4. **Geographical Location**: Coinbase imposes different limits depending on your country of residence. Local regulations and policies can influence how much you are allowed to buy.

5. **Account Activity**: Regular activity and a history of successful transactions can lead to higher limits. If you frequently buy, sell, or trade cryptocurrencies, Coinbase may raise your account limits.

To increase your buying limit on Coinbase, you can:
- Complete all verification steps for your account.
- Add and verify a bank account for higher limits.
- Ensure your account is in good standing and has a consistent history of transactions.
- Check the help section on Coinbase for specific steps based on your country and account status.

By addressing these factors, you can potentially increase the amount you can buy on your Coinbase account beyond the current $100 limit.