Azure SQL Database throwing error 1132 "The elastic pool has reached its storage limit" error, even if it's not full

I'm trying to execute the following (sample) batch in an Azure SQL Database inside an Elastic Pool:
drop table if exists [dbo].[InsertTest];
create table [dbo].[InsertTest] (
[id] uniqueidentifier,
[filler] nvarchar(max)
);

insert into [dbo].[InsertTest] ([id], [filler])
select top 1000 newid(), replicate('X', 2048)
from [sys].[objects] as [T1]
cross join [sys].[objects] as [T2];

/ drop table if exists [dbo].[InsertTest]; /


But the insert statement fails with the error message:
Msg 1132, Level 16, State 1, Line 1
The elastic pool has reached its storage limit. The storage used for the elastic pool cannot exceed (51200) MBs.


I tried to see if I ran out of space by running the query
select
[type_desc] as [file_type],
[size] / 128 as [size_in_MB],
[max_size] / 128 as [max_size_in_MB]
from [sys].[database_files];


but it seems that I still have space left.

file_type
size_in_MB
max_size_in_MB

ROWS
320
256000

LOG
584
1048576

FILESTREAM
0
0

What can I do about it? Am I missing something?

The error message refers to the elastic pool so the problem might relate to another database than the current one. You can retrieve the information about the elastic pool using the following DMV query vs the Master database

SELECT TOP 5 avg_storage_percent / 100.0 * elastic_pool_storage_limit_mb AS ElasticPoolDataSpaceUsedInMB, * 
FROM sys.elastic_pool_resource_stats

StackExchange Database Administrators Q#290042, answer score: 4