For ERC20 tokens, allowance must be checked before tunneling and staking. Before that happens, the submit button can't be enabled, because the code doesn't know if it should request approval or not.

When the user selects a token, the tunnel form loads the allowance. However, while that happens, the submit button is enabled, allowing the user to submit. Generally, this is not a problem, because the allowance data loads fairly quickly. However, if the RPCs are slow, as it's been happening lately, the user could potentially submit the form without the allowance info being loaded, which could cause an error (as it will skip the approve step).

We should check the allowance and disable the submit button until this information is loaded, (perhaps showing a "..." indicating that the info is being loaded).

This is already fixed on the Stake page, but it needs to be applied on the Tunnel.