Welcome to the community!
Sim works alright with Iphone but somehow my samsung s9 plus is not compatible.
It is clear that your SIM card is working fine as it works on your iPhone. There are chances that it is the Smartphone (Handset) it won't be able to detect the SIM card.
Have you tried to do the followin troubleshooting
For additional details, please post a screen shot of the error message of your handset.
Thanks for sending additional information about your SIM card concern.
I would like to arrange a call from one of our Mobile Specialists for further test and investigation.
PM me your best contact number and preferred time today.
I understand that you've been in touch with one of our Mobile Specialists and I can see here that they've arranged a sim replacement for you. This has been ordered last Friday 5, October.
Please note that delivery of the sim will take 2-3 working days for metro areas and 3-5 working days for country locations with Australia post.
Should you need further assistance, please let us know.
We have sent a replacement SIM last 5th of October.
Please notify us once you receive the new SIM card and test if your smart phone will able to detect a signal using the replacement SIM.
Tell us how it will go.
I had the same issue as the topic starter.
Somewhere on Thursday 14 Feb the TPG sim card stopped working in S9+.
Contacted support and got a contact number of the manufacturer - Samsung, to continue the troubleshooting with them.
Before ringing the manufacturer's number, I tried some own "troubleshooting" and found that another provider's sim card works in my S9+. A surprise was also to find out that when the TPG's sim card is installed into an old phone Galaxy A5 and an old type of network is selected - it works too.
Puzzled, rang the TPG support line and provided them with these updates. After some basic troubleshooting (reset network setting, on/off, take out/insert back and etc) was advised that I need to talk to Samsung anyway.
Got a bit emotional on the phone and had requested the case to be escalated to a senior support engineer. The operator advised me that the network engineer would contact me within the next 3-5 working days.
I was already without the phone for more than a week and found it difficult to wait for the fix any longer.
The support line advised that someone would call me in the next 24 hours. That conversation was on Saturday afternoon and today is Tuesday.
I wish I googled this problem before and found this topic I would point out the support team to it and would have had a new sim card on its way.
I was with TPG for a decade and am very grateful for their service along these years. I guess it's just the importance of having the phone communication "always on" became extremely high, escpecially when you have a family to look after and kids who go to uni and schools. I guess, I cannot afford keeping this line disconnected for any longer.
I purchased an Optus new starter kit from Officeworks. Ported my number and got in 10 min my phone/internet back.
So, a piece of advise, if I may - if you find that your tpg sim is working fine in another phone, and another sim is working in your S9+, just ask for the replacement over the phone with techsupport to save time.