The invoice can not be sent for recording since the invoice total amount or accounting lines are not yet signed.
In the parameter Rule for signing account posting line under Administration > Register > Company it is specified what level of control your company is set up to use.
Depending on this setting, check if the invoice's account posting lines are signed. All lines must have a value in the column Signed or all account posting lines must automatically have been checked by Palette in the column Sign for each line.
With the parameter Requirement for signing invoice's total amount under Administration > Register > Company, you setup if the company requires that a role with sufficiently high authorization amount signs an invoice. If this parameter is not used, the authorization is done on the account posting rows only, which means several users can authorize different amounts on the invoice, and send it to final booking without having past a role with an authorization amount big enough to sign the total amount on the invoice.
If you need to change a role's permission, this is done under Administration > General Information > Role or under Administration > General Information > Permissions.