Log query to get a value from a log message and get the average

Question

I have some log messages in my Loki:

2023-02-13 12:20:08.675  INFO 30937 --- [lettuce-epollEventLoop-5-1] c.g.poc.Filter.AuthenticationFilter      : [ requestId : 904c1292-66, AuthFilterTime : 15 ms ]
2023-02-13 12:16:32.100  INFO 30937 --- [lettuce-epollEventLoop-5-1] c.g.poc.Filter.AuthenticationFilter      : [ requestId : f84a572f-65, AuthFilterTime : 4 ms ]
2023-02-13 12:16:31.427  INFO 30937 --- [lettuce-epollEventLoop-5-1] c.g.poc.Filter.AuthenticationFilter      : [ requestId : 904c1292-64, AuthFilterTime : 10 ms ]

I want to get the average value of AuthFilterTime.

I'm getting the error:

"parse error at line 5, col 6: syntax error: unexpected NUMBER"

when i run the query,

sum by (filename)(
  avg_over_time(
    {filename="/path/to/the/log/file"} |= "AuthFilterTime.*ms" |
    regexp `AuthFilterTime\s*:\s*(\d+) ms` |
    $1
  )[24h]
)

Can somebody help what is it that i've been doing wrong??

I'm actually new to grafana.