I take 8000 from slice and pay it back in full before the due date. credit score wont improve. help

i do not own a credit card, however I came across slice a few years ago and wanted to check it out. when I found out that this will get me started on my credit score journey. i took the chance and withdrew 8k and payed it back in full before the due date every month and its been at least a year or two now. however my credit score has always been 729. won’t budge or increase. Will it change if I pay back this low ticket loan with installment instead of in full? How do go about this? any insights would help

how do i shift to better alternative and still keep building my credit score without getting a credit card ?