what bill you paying?

for the failed transaction (without OTP), didnt get charged to HLB.

I retried this morning, gave me "Not Approved" email (got it 1 minute after transaction). However, already charged to my HLB Wise card (within ~15 minues).

Called HLB CS to check all my transactions including yesterday's successful transaction. verified went thru.

very scary

As far as I know, most payee appeared on HLB online service are not entitled for WISE cash back, you can try your luck.
So is better you apply for another cash back card like MBB's dual card. Paying Telekom bills on weekends sure you will be getting 5% of CB and 5X TP(everyday).

Though TM is not listed in any CB category, it is good that you do a real life test to confirm it and update the Wise community here  who knows, you might get a pleasant surprise. 

Like that test rm10 first, balance use MBB.

no issue with my Wise for 1st time payonline use/

1st payment to digi, approved -- 1st time using payonline.
2nd payment to celcom, approved
3rd payment to celcom, unable to process (no TAC) -- rejected by HLB (but captured in the system)
4th payment to celcom (retry), not approved -- rejected by payonline but captured by HLB (unclaimed, floating)
5th payment to celcom (retry), approved -- purposely waited for 7 days later to confirm unclaimed transaction is auto-rejected by HLB.

It seems the "Not Approved" is subjective. No idea why payonline rejected it (almost immediately). The transaction went thru to HLB, captured in the system as floating transaction. From CS' explanation, merchant (payonline) need to claim it first, then only posted to my Wise account. If not claimed within 7 days, that floating transaction will be auto-rejected (CS said 'refunded' back to me).

after 7 days, finally payonline didnt claim from HLB since they already rejected (Not Approve) it at the first place.

i guess this is the internal/system processes between payoline <-> HLB (presumably same with other banks).

the bolded above, same as mine, although it happened on my 3rd payment.

now i probably give some buffer time between each payments.

p/s: I've tried payonline in the evening 7:30pm, it seems it will be "batched" for next morning processing about 9am.
your gsc/wise advice from HLB, interesting indeed  seems like Wise was inactive while GSC was activated. just guessing.