Being unable to submit an additional proposal by either the GRIN user or influencer is typically caused by the campaign settings set to "Non-Recurring" for proposals, which only allows influencers to have one proposal for the campaign.
If you have your campaign set to "Non-Recurring", then your influencers will not able to submit more than one proposal through their Live URL. Also, you will not be able to submit a proposal, on their behalf, from the workroom of the campaign. Attempting to submit a proposal for them in your workroom will result in an error message.
The steps below will guide you through how to adjust your campaign settings to allow for recurring proposals:
Step 1 Click on Program, in the navigation bar, and select Campaigns.
Step 2 Click on the Edit Campaign Details icon.
Step 3 In "Step 1. Campaign Settings", for 'Recurring Proposals' select Recurring.