Your POT would be your safe limit. Any charges over $100 are applied to that limit. You can choose to PIF or the adjusted balance which would lead to interest charges. You can also set up payment plans for charges in the POT with a fixed fee, for a specific amount of time. Anything above your POT limit, and any charges below $100 are due in full on your due date. So as of right now, you should be able to spend at least 6000 with no issue.
Using the Check Spending Ability function would be your best bet. It appears you may be fairly new to credit or have a blemished credit history taking the other approvals into consideration, so your NPSL may not be all that high. You should be able to open a revolving credit card product from American Express now, provided it is approved.
For details on how to use Pay Over Time, Amex has a convenient FAQ. Pay Over Time limits are never disclosed to credit bureaus. Charge cards simply report your statement balance, your minimum payment (which is the same as the statement balance as it is a charge card which by definition has 1 month terms, regardless of POT, balances carried, or other promotional terms), and no limit is reported. Your highest reported balance is used as a credit limit analogue on very old credit scoring models; on modern credit scoring models, they are not factored into revolving utilization. Amex can change Pay Over Time limits, but it's personally never happened to me. I had the same $35,000 on both cards since POT was introduced around 18 years ago.
@Brian_Earl_Spilner wrote:Your POT would be your safe limit. ... So as of right now, you should be able to spend at least 6000 with no issue.
Have the data points changed recently on POT just being a fairly arbitrary number? Historically, we've seen as many people cut off well before reaching POT limits as we have people able to spend well beyond their POT limit.
I'm about 2.5-3 years into my credit journey. So certainly much newer to it than you. lol You have about every AMEX made. lol! That's awesome! 
@PaHi wrote:I'm about 2.5-3 years into my credit journey. So certainly much newer to it than you. lol You have about every AMEX made. lol! That's awesome!
That's not too incredibly new, so as long as your reports are clean and income is both sufficient to support your spending and verifiable within Amex's data collection abilities you likely won't run into issues with NPSL, especially after a bit of time with on-time payments with them.
@K-in-Boston wrote:
@Brian_Earl_Spilner wrote:Your POT would be your safe limit. ... So as of right now, you should be able to spend at least 6000 with no issue.
Have the data points changed recently on POT just being a fairly arbitrary number? Historically, we've seen as many people cut off well before reaching POT limits as we have people able to spend well beyond their POT limit.
I have yet to see anyone cut off before POT limit. Has that become a thing? They asked for a safe limit before charges might be denied. The POT limit should be safe. While they could possibly be allowed to charge 20k, they should be able to charge to 6k without issue since Amex will allow that amount to be carried according to what Amex laid out with their card. If people are being cut off prior to the POT limit, I suspect something triggered their algorithms.
@Brian_Earl_Spilner wrote:
@K-in-Boston wrote:
@Brian_Earl_Spilner wrote:Your POT would be your safe limit. ... So as of right now, you should be able to spend at least 6000 with no issue.
Have the data points changed recently on POT just being a fairly arbitrary number? Historically, we've seen as many people cut off well before reaching POT limits as we have people able to spend well beyond their POT limit.
I have yet to see anyone cut off before POT limit. Has that become a thing? They asked for a safe limit before charges might be denied. The POT limit should be safe. While they could possibly be allowed to charge 20k, they should be able to charge to 6k without issue since Amex will allow that amount to be carried according to what Amex laid out with their card. If people are being cut off prior to the POT limit, I suspect something triggered their algorithms.
It used to be a thing, at least. Lower amounts seem to be a more recent thing, but back when $25k and $35k seemed to be the standard POT amount it was generally understood that they weren't a reliable indicator of spending ability in either direction.
