I claimed the seasonal Chapter 1 reward, but no item appeared in my inventory.
There is no reward for chapter 1. Rewards start from chapter 2 (read the seasonal blog for details).
The mail you got is likely this one; nothing to be claimed:
2 Likes
In addition to what Maskraider said, you should consider checking the stickied threads before creating a new one…
yo ya reclame la recompensa de temporada, pero las armaduras que dan de recompensa no le llegaron al inventario de mi pj (monje mujer)
Not a bug. Read the season post on home page. It explains the Haedrig’s gifts.
Chapter 1 reward - no chest
And you were answered here:
You do not receive a reward for completing only Chapter 1. You must complete Chapter 1 and Chapter 2.