If you're trying to meet MSR on a CIP by paying student loans, I'd really suggest using Plastiq instead.
As you noticed, GoC gift cards max out at $200 but has an activation fee of $5.95 per card. As far I'm aware, you can apply as many GoC cards to your account as you want, but you'll be paying a 2.975% fee on each card. Toys R Us/Babies R Us used to sell GoC gift cards loadable up to $500 for a $5.95 activation fee (1.19%), but that's gone. Some regional grocery stores still carry variable load GoC cards up to $500 (I'm thinking HEB), but those may not be available to you. There have been rumors for almost 2 years now that GoC cards will be available at
Best Buy.
Plastiq has a 2.5% credit card fee, so already cheaper than $200 GoC cards. But on the CIP, Plastiq earns 3x UR for every type of payment -- including student loans -- and the fee. (There's no restriction to paying student loans with Visa cards on Plastiq, but student loan payments are generally not allowed with Amex.) So for example, if your student loan payment is $500/month, you'd pay a 2.5% fee or $12.50; but as long as Plastiq earns 3x UR on CIP, you're earning 3x UR on $512.50 or 1537.5 UR, which is worth $15.37 if you cash out with a statement credit or bank deposit or worth 1.25x more ($19.22) towards travel if you transfer and redeem the UR points to CSP/CIP, or 1.5x more ($23.06) on the CSR. So with Plastiq, you're paying a 2.5% fee, but you're coming out ahead of that fee if you're paying with the CIP.
If you decide to use Plastiq, please consider signing up through a DISchurners link. You'll support a fellow member, but you'll also get $500 fee free dollars ("FFDs") after you make your first $500 in payments. That means the next time you use Plastiq, they'll waive the fees on your next $500 worth of payments (saving you $12.50).