The payment is failing because it has opened a channel where node 1 has 10000 sat, and node 2 has 0 sat, and then tries to make node 2 pay node 1.
From what I understand, in point 4 you try to make node 2 & # 39; add funds & # 39; to the channel that you opened in step 3. This is not how a lightning channel works: a lightning channel is a bitcoin UTXO, and you can not add it to it. bitcoins to an existing UTXO. Each channel is defined when it is created, and then it is resolved when it is closed (the appropriate balance is sent to each participant).
Taking into account your configuration, you can make a payment from node 1 to node 2. Once this is done, you can make payments from node 2 to node 1 (until the entire balance is returned to one side).
What you could also do to achieve a similar result is to open a new channel from node 2 to node 1. I'm not familiar with c-lightning, but I know that LND allows you to open two channels with the same pair. As mentioned, double financing is possible but has not yet been implemented.