Serve Not Allowing Non-Amex Cards
I broke the news last month that credit card loads from non-Amex cards to Serve will end on April 16, 2015. This means that you still have a chance to max out your $1k ($1.5k for Softcard version) limit for the month.
Unfortunately several users on Reddit are reporting that American Express has already updated their system to prevent the addition of non-Amex cards. This means that the only way a non-Amex credit card load will work is if you use a card already linked to your Serve account.
At this point I would highly suggest not deleting the current card linked to your Serve account. While some people reported they were able to add a new card in the past couple of days, quite a few have had issues and thus are missing out on their last loads.
Let me know in the comments if you have had similar issues!